(Reuters - Mon Aug 18, 2014) - Community Health Systems Inc, one of the biggest U.S. hospital groups, said it was the victim of a cyber attack that originated in China, resulting in the theft of personal data belonging to 4.5 million patients in April and June.

The stolen information included patient names, addresses, birth dates, telephone numbers and Social Security numbers of people who were referred for or received services from doctors affiliated with the hospital group in the last five years, it said in a regulatory filing on Monday.

Community Health Systems spokeswoman Tomi Galin said the company believes the attack originated from China because federal law enforcement and forensics experts with FireEye Inc unit Mandiant had told it that "the methods and techniques" employed by the hackers were consistent with a particular group of hackers operating in China.

Galin did not identify the group by name or say if it was believed to be linked to the Chinese government.

In May, a U.S. grand jury indicted five Chinese military officers on charges that they hacked into U.S. companies for sensitive manufacturing secrets, the toughest action taken by Washington to address cyber spying to date. China has denied the charges.